Several studies were made of different aspects of the morphology of bioprosthetic cardiac valves: 1) in one of these studies 1% benzyl alcohol in Dulbecco's solution was found to be a satisfactory storage medium in which to keep explanted bioprosthetic heart valves that need to undergo both functional testing and morphological study. Valves kept in this solution retain adequate morphology and do not become excessively stiff (as do valves kept in aldehyde-containing fixatives); 2) Extensive reviews were made of the morphology of collagen in unimplanted and explanted bioprosthetic heart valves, of the anatomic changes that bioprosthetic valves undergo as the result of preimplantation processing, and of the pathological changes that develop after these valves are implanted as substitute cardiac valves in patients with valvular heart disease.